The invention relates to a method for non-destructively testing construction elements by measuring their resonant vibrations.
The invention is intended primarily for quality control and damage analysis to test and monitor construction materials and components. Unwanted joint changes and cracks can occur in the manufacture and handling or stressing of construction components. To prevent them from subsequently failing it is necessary to examine and detect these changes without destroying the component.
It is known that joint changes in construction components affect the modulus of elasticity, the density, the transverse contraction and influence the distribution of sonic transmissions. When a component is caused to vibrate characteristic resonances occur as a result of its geometry, which provides information about the condition of the component. This also applies to the formation of cracks because this causes a change in the spring/mass-system. These flaws produce changes in the formation of vibration characteristics of the component.
The known test methods which operate with ultrasonic radiation rely on sending a sonic impulse into the component and measuring changes in its reflected echo caused by flaws in the component. In these methods the transmitted impulse has a constant frequency and must decay as quickly as possible so that the echo, which is reflected by the back wall of the component or the flaws in front of it, can be received. To this end it is necessary that the transmitted impulse strike the flaw as directly as possible. To detect internal flaws a component must be scanned along its surface. Flaws can only be recognized if they can be directly reached by the transmitted signal. Therefore, it is desirable for rapid flaw detection in components to use a method which makes integral measurement of hidden flaws in the component possible.